1. Field of the Invention
The present invention pertains to a hydrodynamic clutch device, especially to a hydrodynamic torque converter or fluid clutch, comprising a housing unit; a turbine impeller rotating around a rotational axis in the housing unit; and a bridging clutch unit, which has a clutch element connected in essentially nonrotatable fashion to the turbine impeller. A friction area of this clutch element can be brought into frictional contact with an opposing friction area provided on the housing unit.
2. Description of the Related Art
In hydrodynamic clutch devices designed in this way, it is known that, in order to actuate the lock-up clutch unit, that is, to produce or to release the essentially direct torque-transmitting connection between the turbine impeller and the housing unit, the pressure relationships inside the housing unit must be adjusted in such a way that either the friction area of the clutch element is pressed more strongly against the opposing friction area or that this mutual frictional contact is released. For this purpose, there must be a positive pressure of at least 1 bar inside the housing unit, in some cases as much as 2 or 3 bars. This requires a correspondingly high pressure-generating capacity, that is, delivery capacity, and thus to a relatively expensive design.
It is also known that the clutch element, which is designed essentially as a ring-shaped disk and is made of sheet metal, can be attached by its radially inward area to the turbine impeller by rivets or welds, for example, and to design it with a contour or shape which allows its own elasticity to pretension it toward the housing unit, i.e., to pretension its friction area toward the opposing friction area. Providing a pretensioning force of this type already provides a certain baseline frictional interaction, so that the increase in pressure required to produce a bridging state does not have to be as large. In this type of design, in order to produce the non-bridged state, an opposing pressure must be built up in the area between the clutch element and the housing unit not containing the turbine impeller, this opposing pressure working ultimately against the inherent preload of the clutch element.
This arrangement suffers from the disadvantage that, to obtain a sufficiently stable arrangement, the clutch element must be designed with a comparatively high degree of stiffness. This means that the pretensioning force is also correspondingly large, and ultimately the opposing force, which must be generated to produce the unbridged state, is again associated with the need to provide a fluid feed pump of relatively high capacity.
It is the task of the present invention to provide a hydrodynamic clutch device in which a comparatively small pressure change in the housing unit can initiate or to release the torque-transmitting state between the housing unit and the turbine impeller produced by the use of the bridging clutch unit.
According to the present invention, this task is accomplished by a hydrodynamic clutch device, especially a hydrodynamic torque converter or fluid clutch, comprising a housing unit; a turbine impeller rotating around a rotational axis in the housing unit; and a bridging clutch unit, which has a clutch element connected in essentially nonrotatable fashion to the turbine impeller, this clutch element being provided with a friction area which can be brought into frictional contact with an opposing friction area on the housing unit.
The hydrodynamic clutch device according to the invention also has a pretensioning unit, which acts on the clutch element to pretension it toward the opposing friction area.
By providing the pretensioning unit, it is also guaranteed that a certain baseline contact already exists between the friction area and the opposing friction area, regardless of the pressure relationships which have been established. Because a pretensioning unit separate from the clutch element is provided here, the pretensioning force produced by it can be adjusted independently of how the clutch element itself is designed. This means that the pretensioning force can be adjusted so that only a comparatively small release force, generated by fluid pressure and acting against the pretension, is required to actuate the clutch element for the purpose of releasing the mutual frictional contact. This has the result that fluid feed pumps of considerably smaller delivery capacity or significantly smaller pressure-generating capacity can be used and that the entire environment in which a hydrodynamic clutch device of this type is used can thus be built in a more cost-favorable fashion.
For example, the pretensioning device may include at least one pretensioning spring element, the force of which acts between the clutch element and the turbine impeller.
This pretensioning element, at least one of which is provided, can comprise a leaf spring element, which is permanently connected by at least one attachment area to the turbine impeller or to the clutch element, and which also has an actuating area, which acts on the other unit, i.e., either the clutch element or the turbine impeller. Leaf spring elements of this type can be produced at very low cost and in particular show uniform elastic and force characteristics in operation over a long service life.
The leaf spring element is preferably attached permanently to the turbine impeller, such as to the hub of the turbine impeller. This offers the advantage that, in the area of the clutch element itself, no connecting measures for producing a permanent connection, such as a riveted connection, must be taken. As a result, no leaky areas which could allow the undesirable exchange of fluid between the two fluid chamber areas in the housing unit separated by the clutch element are produced on the clutch element itself.
In a further embodiment, the pretensioning spring element, at least one of which is provided, may include a disk spring element, a corrugated spring element, or the like, which is supported on the turbine impeller, preferably on the hub of the turbine impeller, and the clutch element.
In a further embodiment, at least one pretensioning spring element acts between the clutch element and a driver element, which element is provided on the hub of the turbine impeller and is in torque-transmitting engagement with the clutch element. This driver element can be provided in a radially outward area of the turbine impeller, and it can be in torque-transmitting engagement with a radially outward area of the clutch element.
To ensure that suitable surface-to-surface contact not impaired by any type of deformation is achieved when the clutch element produces frictional contact between itself and the housing unit or the opposing friction area, it is proposed that the clutch element be essentially rigid. The phrase xe2x80x9cessentially rigidxe2x80x9d in the sense of the present invention means that it is not necessary for the clutch element to undergo any deformation to produce or to release the torque-transmitting connection between the turbine impeller and the housing unit. Instead, the clutch element should be so rigid that, aside from the minimal deformations necessarily present as a result of the forces acting on it, it is made available for interaction with the housing unit or the opposing friction area essentially in its original, as-produced shape, so that suitable frictional contact is always guaranteed between the friction area and the opposing friction area.
To guarantee also the required axial movement of the clutch element, at least in the part carrying the friction area, the clutch element can be movable with respect to the turbine impeller in the direction of the rotational axis. For this purpose, the clutch element can be mounted on the turbine impeller, preferably on a turbine impeller hub, in an essentially fluid-tight manner, so that it can be shifted in the direction of the rotational axis.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.